Crystal structures of two tandem malectin‐like receptor kinases involved in plant reproduction

摘要

Complex cell‐to‐cell communication between the male pollen tube and the female reproductive organs is required for plant fertilization. A family of Catharanthus roseus receptor kinase 1‐like ( Cr RLK1L) membrane receptors has been genetically implicated in this process. Here, crystal structures of the Cr RLK1Ls ANXUR1 and ANXUR2 are reported at 1.48 and 1.1?? resolution, respectively. The structures reveal a novel arrangement of two malectin‐like domains connected by a short β‐hairpin linker and stabilized by calcium ions. The canonical carbohydrate‐interaction surfaces of related animal and bacterial carbohydrate‐binding modules are not conserved in plant Cr RLK1Ls. In line with this, the binding of chemically diverse oligosaccharides to ANXUR1 and HERCULES1 could not be detected. Instead, Cr RLK1Ls have evolved a protein–protein interface between their malectin domains which forms a deep cleft lined by highly conserved aromatic and polar residues. Analysis of the glycosylation patterns of different Cr RLK1Ls and their oligomeric states suggests that this cleft could resemble a binding site for a ligand required for receptor activation of Cr RLK1Ls.